Tissue products must reconcile many competing qualities; they must be strong yet soft, absorbent yet protective, and above all, they must be inexpensive. This invention relates to a method of making tissue products more protective without adding inordinately to the cost while retaining the ability for the sheets to be flushed or repulped as well as the resulting tissue. Many methods of imparting barrier properties to tissue products involve adding a sizing agent to the furnish, or some part of the furnish, before the sheet is formed and result in permanent hydrophobicity which often makes flushing problematic and repulping impractical. Further, wet end addition usually implies that sizing must be applied over the entire area of the sheet of tissue and may impose limitations on the other additives that can be incorporated into the furnish. In approaches where the sizing agent is applied after the sheet is formed, additional drying may be required in many cases, which may either add greatly to the cost or be completely impractical depending on the manufacturing facilities available. Further, addition of even relatively small amounts of water to a previously formed tissue sheet can greatly detract from desirable properties that the tissue maker has gone to great lengths to incorporate into the sheet—particularly bulk and softness.
Some of the most potent sizing agents for papers are reactive sizes. These are extremely efficient and have become very widely used, at least for flat papers and paperboards. While there have been many methods proposed for using reactive sizes as an internal size for tissue products, use as external size has been hampered by the difficulty involved in getting the reactive agents onto the sheet without seriously detracting from the structure of the tissue as well as potential difficulty with flushing or repulping the resulting sheet. In the typical case, heat is applied after the reactive size has been applied to ensure that they accomplish exactly what is implied by “reactive size”—to react with the sheet, typically by opening the β-lactone ring followed by esterification in the case of alkenyl ketene dimers or, in the case of alkenyl succinic anhydrides, by ring opening of the anhydride ring also followed by esterification. However, in almost all cases, after reactive sizes are applied either as emulsions or by incorporation in the wet end, heat is applied to open the ring structure and drive the esterification reaction to completion imparting permanent barrier properties to the treated sheet and thereby potentially interfering with repulpability and flushability.
Accordingly, it can be appreciated that there has been a need for towel and tissue products having barrier properties but retaining flushability and repulpability with premium grade softness that could be easily manufactured on existing manufacturing assets.
McConnell et al., U.S. Pat. No. 6,573,203, discloses:                . . . a towel desirably including first and second layers having cellulosic fibers and a repellant agent. The first and second layers may substantially sandwich a third layer having cellulosic fibers with higher absorbency than the first and second layers. All three layers may form a single ply.        Furthermore, the towel may also include fourth and fifth layers positioned between, respectively, the first and third layers and the second and third layers. The fourth and fifth layers may have cellulosic fibers with higher wicking than the first and second layers.        In addition, the repellant agent may be wax, latex, a sizing agent, and/or silicon. Moreover, the repellant agent may be printed and/or sprayed onto at least one of the first or second layers. Furthermore, the repellant agent may be mixed with the fibers of at least one of the first or second layers in a headbox. What is more, the first or second layers may include sulfite pulp or BCTMP and the towel may have a basis weight from about 8 gsm to about 59 gsm. [col. 3, 11. 8-26]        . . . Repellant agents may include waxes, latexes, silicon, and sizing agents. [col. 4, 11. 33-34.]        . . . Particularly suitable sizing agents are acid or alkaline sizes such as acid rosin, alkenyl succinic anhydride, alkyl ketone dimers and alkenol ketene dimers . . . [col. 2, 11. 5-7]        
Hsu et al., U.S. Pat. No. 6,332,952, discloses a tissue having at least one ply with a region that prevents fluid from striking through the tissue product stating that:                Furthermore, at least one ply may be treated with a repellant agent to create a region for preventing fluid strikethrough. Moreover, at least one ply may be printed and/or sprayed with a repellant agent. In addition, the repellant agent may be a sizing agent or hydrophobic chemical.        Another embodiment of a toilet tissue product may include a first cellulosic ply further having a first layer and a second layer and a second cellulosic ply further having a first layer and a second layer. The first layers of the plies may substantially sandwich the second layers of the plies, where at least one of the second layers may be resistant to fluid strikethrough. In addition, at least one of the second layers may include a repellant agent.        Moreover, the repellant agent may be a wax, latex, hydrophobic chemical and/or sizing agent. Furthermore, the repellant agent may be printed onto at least one of the second layers. Additionally, the repellant agent may be sprayed onto at least one of the second layers. Also, the repellant agent may be mixed in with the fibers of at least one of the second layers in a headbox. Further, at least one of the second layers may include sulfite pulp or BCTMP. [col. 3, 11. 33-54]        Particularly suitable sizing agents are acid or alkaline sizes such as acid rosin, alkenyl succinic anhydride, alkyl ketone dimers and alkenol ketene dimers . . . [col. 2, 11. 29-32]        . . . A repellant agent, such as a sizing agent, may be applied to the dry web by spraying an aqueous solution through the spray boom 148 located between the blade 144 and the core 152. Alternatively, the repellant agent may be sprayed or coated onto the moving tissue web prior to the pressure roll 130 or after the tissue web has transferred to the Yankee dryer 136. [Col. 6, 11. 57-63]        
A variety fluorinated AKD and ASA derivatives have been used as sizes to impart resistance to both oil and water. Bottorff; U.S. Pat. No. 5,252,754, suggests the use of a:                . . . class of sizing composition . . . referred to as fluorinated alkyl ketene dimer dispersions/emulsions and represented for convenience by the abbreviation RfAKD. The invention particularly contemplates their use to impart water, hot-water, oil, and hot oil resistance to biodegradable cellulose molded articles, thus providing an alternative to non-biodegradable polystyrene. [col. 4, 11. 34-41]        
Bottorff further teaches that:                The aqueous RfAKD dispersions/emulsions are very stable. Outstanding oil, grease and water resistant paper can be achieved by convenient, direct addition of the RfAKD dispersions/emulsions to the pulp slurry as the paper is being made or by surface application after the paper is formed. The RfAKD can also be surface applied to preformed paper from an organic solvent solution. They are not precipitated by cations from hard water, unlike the anionic salts contained in commercial oil-sizing agents, and the use of water softening agents is avoided.        The RfAKD sizing agents of the invention form covalent bonds to cellulose fibers under conditions existing on commercial paper machines using the heat from the paper machine, and thus avoid disruption of the bonding by acidic, basic, or neutral aqueous penetrants. [col. 6, 11. 7-22]        
Harrison et al., U.S. Pat. No. 5,714,266, suggests use of:                . . . a composition for treating pulp slurry in the wet end comprising (A) a mixture of fluoroaliphatic radical-containing phosphate esters comprising at least 70% of phosphate monoesters, e.g.        C8F17S02N(C2H5)C2H40P(0) (OH) (0−NH4+) and (B) an alkyl ketene dimer, e.g. Hercon™ 76 from Hercules. Preferably, said mixture of esters comprises greater than 90% of said monoester.        
Harrison et al. further suggests use of:                . . . a method for preparing treated paper and paperboard products comprising (1) treating pulp slurry in the wet end with the composition of this invention. and (2) curing this treated slurry using low heat conditions (e.g. ambient temperature up to 250° F.) and high moisture content (e.g. greater than 10%) to give a treated paper or paperboard. [col. 2, 11. 6-19]and teaches that:        This invention provides treated paper and paperboard exhibiting superior resistance to both microwave soups and oils within two hours of drying. This unexpected behavior is most dramatic with pulp slurries containing a high level of post-consumer waste and/or fines, as these slurries typically are more difficult to treat than virgin fiber to achieve resistance to soups and oils. This invention gives an unexpected boost in water sizing performance compared to when the alkyl ketene dimer is used alone, especially in making molded pulp items such as microwave trays, take-out food trays and egg cartons. These items are made from very diverse furnish types (I.e. blends of softwood and hardwood fibers along with clay fillers and binders), may contain up to 100% recycled fiber, and are generally incompletely dried during the cure cycle. [col. 2, 11. 23-37]        
Harrison et al. presents data purporting to show that:                . . . the fluoroalkyl monophosphate ester of Example 23 had excellent Soup Test and Oil Test result even when no heat cycle was employed. i.e. the treatment was allowed to cure at room temperature. In contrast, cured under the same ambient conditions, the fluorochemical paper treatments of Comparative Examples CI4-C 16 all had poor Soup Test results, and the alkyl ketene dimer (Hercon™ 76) used alone (Comparative Example C17) had poor Oil Test results. [col. 11, 11. 48-55]        
This last teaching is generally in concert with the teaching in Kern, U.S. Pat. No. 5,308,441, that:                . . . synthetic sizing agents such as alkyl ketene dimer, stearic anhydride, and alkenyl succinic have been developed to form true chemical covalent bonds with cellulose rather than the ionic or polar bonds of natural size. Most prevalent of these synthetic size compounds is alkyl ketene dimer (AKD). Once cured, synthetic size is more stable against water, acids, and alkalis . . . [col. 1, 1. 65-col. 2, 1. 4]        
England et al., U.S. Pat. No. 3,362,965, relates to beta-lactones of 3-hydroxy-4,4-bis(perfluoroalkyl)-3-butenoic acids and states that:                A few drops of the above β-lactone of Example I [β-lactone of 3-hydroxy-4,4-bis(trifluoromethyl)-3-butenoic acid] were placed on a filter paper, and the paper along with a control piece (nothing added) was warmed with hot air until it appeared dry. Both pieces of paper were then dipped into a beaker of water. It was immediately obvious where the added drops of lactone had reacted with the paper as only this portion was not saturated by the water even after several minutes soaking. When removed from the beaker, water drained from the treated portion of the paper which remained dry but the untreated paper was wet throughout. [col. 4, 11. 34-44]        
Endres, European Patent Application 0144658, relates to:                . . . a tissue product comprising an internal porous barrier layer or ply of papermaking fibers coated with a water repellent agent [that] prevents or inhibits wetting of the user's hands during use and at the same time significantly improves the in-use strength of the product. [p. 1, 11. 29-34]        
Endres teaches that:                . . . when a user blows his nose into a three-ply facial tissue of this invention having an inner layer comprising papermaking fibers coated with a water repellent agent, the nasal discharge will be absorbed by the outer ply touching the nose (the first outer ply), but will be inhibited from contacting the hands touching the other outer ply (the second outer ply) because the barrier layer retards fluid transmission. Therefore, by delaying or reducing the amount of moisture that reaches the second outer ply, the second outer ply retains much or all of its dry strength and therefore the tissue as a whole remains stronger in use. Hence the tissue will not fall apart in use as easily and the user's hands will be less likely to get wet. [p. 2, 11. 2-15]                    . . .                        The water repellent agents useful for purposes of this invention can be any chemical which will coat a cellulosic fiber and increase the wetting angle of aqueous fluids which contact the surface of the fiber. There are many types of such water repellent agents which can be used for this purpose and are well known in the chemical arts. Examples of water repellent types include: wax dispersions with or without aluminum or zirconium salts; metal salts and soaps; pyridinium repellents; waxy thermosetting resins; organometallic complexes of chromium and aluminum; silicones; fluorochemicals; and alkyl ketene dimers. Those skilled in the art will appreciate that the suitability of any specific water repellent agent will depend greatly on a wide variety of factors other than technical feasibility, such as economics, processing considerations, toxicity, etc.        In preparing the products of this invention, it is preferable that the water repellent agent be mixed with the papermaking fibers prior to formation of the web . . . [p. 3, 11. 2-21]        In any case, however, regardless of the manner in which the web is formed, the water repellent agents can be printed or sprayed onto the surface of a web to create a surface layer of water repellent fibers on the web. This can be advantageous for a two-ply product, for example, where the inner surface or surfaces of either or both plys can be coated with the water repellent agent to create the internal water repellent layer. In such a situation, however, care must be exercised not to allow the water-repellent agent to soak entirely through either of the plys and thereby detrimentally affect the absorbency and feel characteristics of the outer surface of the treated ply. Naturally this is more difficult to control with lower-basis weight webs as are commonly used for two-ply facial tissues. [p. 4, 11. 1-15]        
The aforementioned references are incorporated herein in their entireties.